Runtimes offer services to executing applications while those applications are running. Runtimes often specialize in the domain of applications that they serve. For instance, presentation runtimes tend to serve applications that are oriented toward presentation. WINDOWS® Presentation Foundation (WPF) is an example of a presentation layer that serves as a presentation runtime. Workflow runtimes, on the other hand, tend to serve applications that are reliant on sophisticated application control. WINDOWS® Workflow Foundation (WF) is an example of a workflow runtime.
The operation of WINDOWS Presentation Foundation (WPF) and WINDOWS Workflow Foundation (WF) are both driven by XAML documents, albeit each runtime uses a different schema of XAML in order to operate. As a side note, the XAML specification introduces several concepts, two of which are of particular note here. One concept is referred to as “markup extension”, which is an object that derives from the System.Windows.Markup.MarkupExtension abstract class. In general, the XAML parser treats a markup extension as it would any other object. However, the XAML parser calls the markup extension's ProvideValue method to produce the final object, rather than simply inserting the markup extension object directly. The second concept is referred to as the “x:Name attribute”, which uniquely identifies object elements for access to the instantiated object from code-behind or general code. Once applied to a backing programming model, x:Name can be considered equivalent to the variable holding an object reference, as returned by a constructor. While markup extensions and x:Name attributes are known, they have not been used together in a way that integrates WPF and WF, but are used for different purposes entirely.
The WPF runtime is strong in presentation, while the WF runtime is strong in underlying control. However, there is no conventionally known way to integrate these runtimes for applications that want the sophisticated presentation offerings of WPF while also providing the strong execution logic and control afforded by WF.